An acrylic acid is produced by partially oxidizing propylene and then oxidizing tile resulting acrolein. This process is performed at the lowest possible oxygen concentration in order to maintain high selectivity of acrolein or acrylic acid, as well as to avoid the combustion resulted from the increased oxygen concentration in tile reactant and to prevent excess reaction. Complete oxidation such as production of CO and CO2 at an elevated temperature causes reduction of the selectivity toward acrolein. Further, elevated reacting temperatures cause inactivation and volatilization of the active components and reduce the lifetime of the catalyst as well. Thus, if catalysts for preparing an acrylic acid have higher activity at a lower reaction temperature and higher selectivity toward the acrylic acid, they have higher commercial values.
A number of patent applications, which relate to catalysts used to produce acrolein by gas phase oxidation of propylene, have been filed to meet the commercial demands. For instance, U.S. Pat. No. 2,941,007 (J. L. Callahan et al.) discloses a catalyst comprising bismuth molybdate or bismuth phosphomolybdate. U.S. Pat. No. 3,171,859 (K. Sennewald et al.) discloses a catalyst consisting of Fe, Bi, P, Mo and O. U.S. Pat. No. 3,522,299 (S. Takenaka et al.) discloses a catalyst consisting of Ni, Co, Fe, Bi, Mo, P, As and O. U.S. Pat. No. 3,089,909 (J. L. Barclay et al.) discloses a catalyst selected from the group consisting of tin tungstate, tungstic acid and bismuth tungstate. In addition, U.S. Pat. No. 3,825,600 (T. Ohara et al.) discloses a catalyst containing Mo, Co, Fe, Bi, W, Si, alkali metal etc.
Even though some of these catalysts do not have yields sufficient to produce acrolein and acrylic acid to be applicable to the industry, improved catalysts have been proposed. For example, U.S. Pat. Nos. 4,873,217, 4,224,187, 4,248,803, 5,017,542 etc. proposed catalysts which have a higher conversion rate of propylene and improved yields of acrolein and acrylic acid by controlling the ingredients of a catalyst and their mixing ratio, and processes for producing the catalysts.
On the other hand, there have been developments in the methods for producing a acrolein and acrylic acid utilizing conventional catalysts of molybdenum-bismuth-cobalt-iron oxide compounds. However, further studies are increasingly needed to develop a process for producing a catalyst of molybdenum-bismuth-cobalt-iron oxide compounds which has higher activity and selectivity.